


Dead Air

by TheRechercheRambler



Series: A Chance Meeting [3]
Category: Undertale (Video Game)
Genre: Alternate Universe - Underfell, Implied/Referenced Child Abuse, Not a Crossover, Underfell is not a good place for kids to be brought up, and also child neglect, and now you'll know... the rest of the backstory, but it's the Underfell equivalent of a few FTA chapters, it's time for me to stop dancing around the issue and address the Gaster-shaped elephant in the room, takes place between A Path to Redemption and A Peculiar Crossroads, this fic is full of flashbacks, this is a companion piece to A Chance Meeting and not directly related to From Thinnest Air
Language: English
Status: Completed
Published: 2016-04-17
Updated: 2016-04-17
Packaged: 2018-06-02 21:15:36
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 3
Words: 4,469
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6582709
Author URL: https://archiveofourown.org/users/TheRechercheRambler/pseuds/TheRechercheRambler
Summary: <blockquote class="userstuff">
              <p>Six months after monsterkind reaches the surface, a certain few discover that memories, too, are resurfacing.</p>
            </blockquote>





	1. Closely Kept

Dr. Alphys, ex-evil genius but full-time mad scientist, was deep beneath Mount Ebott, within the Core that had once sustained monster civilization. She was scouring the vast complex for files and technology that had been abandoned when they'd escaped the Underground. In their eagerness to get out, to put their dusty past behind them, start again, and create new, less violent lives for themselves, they'd left a lot behind down in their old dwellings. For six months, everyone had been hesitant to go below again. The Underground had once been the prison of monsters; emptied of its former inmates, it now imprisoned the memories of the darkest moments of their history.

But as time passed, as they struggled together to thrive on the surface, they once again had to descend to the roots of the mountain to bring up to the light what they'd left behind if they were going to keep making progress.

For Alphys, this meant gathering up all sorts of things; machines, gadgets, weapons (if only to repurpose them for defense), blueprints, reports, lab data, and other files. The monsters she and the old Royal Scientist had tried to strengthen frequently had unique magical and medical needs; they'd managed this long, but it was getting hard to go on without the files on them that described all the ways that they'd been changed. As hard as it was for the doctor to confront her old experiments again, it was up to her to try to keep them going and make things right; it was usually Alphys's fault, after all that the subjects were the way they were.

Once she'd finished scavenging in the True Labs with help from some volunteers (several of her friends among them), she'd moved on to the Core. She mostly expected to salvage its equipment or perhaps cannibalize it for parts for future machines. Thankfully, its moving mechanisms had shut down with the rest of it, so its rooms and corridors could no longer shift about- even after becoming Royal Scientist Alphys had had a hard time making sense of it. Sans, strangely, seemed to be finding his way around without any trouble; but then again, he seemed able to find his way around everywhere, or at least was very good at acting like it.

As such, it had been only mildly surprise when Alphys had come across a door to a room she'd never noticed before. When she'd opened it, she'd been met with total darkness and the stench of stuffy dead air. Lights feebly flickered on when she flipped a wall switch, and even as she banished the murky shadows she couldn't shake the feeling that something was watching her from deep inside the room.

It was a small lab room of some sort, with a lone desk, a few workbenches, and some sort of examination table. Years of disuse were plainly seen in the grime that had accumulated thickly upon everything in the room- the desk, the table, even the smattering of scribbled notes so haphazardly strewn about the room Alphys might've thought a tiny tornado had hit them.

What was this place?, Alphys wondered. She'd never worked in there, never even heard so much as a rumor of it. Had it belonged to her predecessor? Strange as it was, she was certain that she'd never met the monster that had been Royal Scientist before her. In spite of her long years of work, moving up from lackey to assistant to researcher to mad scientist proper, she couldn't recall ever meeting her boss. They must have still held the post when she started making her way among the Underground's cutthroat scientific community. She had some vague idea that the position had been vacant for a long time, but surely not that long? There was a piece missing in that puzzle that Alphys had never been able to find.

She plodded over to the desk, curious at what she might find. The notes, sadly, were all illegible, but maybe there was something of interest inside the desk. Alphys pulled a few drawers open with trembling claws- still the watchful feeling would not go away!- but found only things like instruments, duct tape, and spare pencils. Not even so much as a small personal object, like a picture, that might give her some hint of who might have once worked there. For all she knew it hadn't been occupied since before the Queen's children had died.

With a disappointed huff, Alphys checked the last drawer, yanking it open, and her eyes widened. This one, at least, wasn't entirely empty- it was oddly brimming spare notepads. Her yanking had disrupted them, and as she peered inside she saw a single file, which must have been carefully concealed beneath the notepads. She eagerly pulled it out, and her eyes practically popped out of her head. She'd know that type of file anywhere- it contained files on a subject of enhancement experiments. What on Earth was it doing outside of the True Labs? Even without opening it the thing posed a very troublesome puzzle.

Even just by looking at it unopened the file made as little sense as the monster whose name it bore. All files on test subjects had been kept down in the True Labs, for the Royal Scientist's and their chosen assistants' eyes only. Yet this had been kept hidden in a small workshop that Alphys, for all her years working in the place, had never seen before. Besides that, files on test subjects never bore the subject's real name on the tab- they had the subject's ID, and their real name was listed on an inside paper, if it was listed at all. This monster didn't even seem to _have_ a Labs ID.

Alphys exhaled slowly. Improper protocol aside, it was the subject of the file that left her with the biggest mystery of all.

Since when had _Sans_ ever been part of a magic enhancement experiment?

It did help her understand a few things, she supposed; how he could find his way around the Core and True Labs as if he'd known them for years, how he understood so much more of the scientific ideas she'd discussed than any of the others even though he professed not to be interested in science, and perhaps even how his powers were so varied in spite of his general magical output being so weak. But still, _Sans_?

She was faced with more questions than answers- when had this happened? Why? How come Alphys had never heard anything about it?

And how had Sans gotten away, when Alphys and her predecessor had never allowed their subjects to go back to regular Underground society? Her predecessor, so she gathered from their scant reports, had wanted to prevent other monsters from trying to be strengthened before the process was ready, and to keep word from getting out of the failures. Alphys had wanted the same, but besides that, she knew that if they were let out her subjects would be torn apart the second they got into even a small skirmish thanks to their weaknesses.

Had Papyrus been involved? Did he have a file? If he did, where was it, since Sans's file been stored in such a strange place? Why was it unique? Who the hell was Sans?!

A part of Alphys wanted desperately to open it up and wrest the answers from it, but something stayed her hand.

“find s-something?” a voice asked lightly behind her.

Alphys froze, and her breath caught. She hadn't heard Sans arrive. Strangely, he sounded just as nervous as she felt.

“I didn't open it!” she blurted out as she whirled around, eyes wide, still clutching the file in a vice-like grip.

Sans tensed up when he saw what she was holding, teeth bared in a taut grin. His pupils shrank to mere pricks of light.

“where did you get that?” he asked in a low voice.

“In one of the drawers. I was just trying to figure out w-what this place was!” she said defensively. Was that a crime!? It wasn't like she'd been _trying_ to pry into his secrets or anything like that. …Not initially, at least.

“give it to me.” Sans demanded. He stepped forward, clearly intending to take it however necessary. Alphys held the file out at arm's length. The skeleton quickly snatched it away from her.

“Sans… w-what…?” The question died in Alphys's throat as the skeleton watched her. She gulped nervously.

“welp. paper shredder's gonna claim another victim today.” Sans said conversationally, but still gave Alphys a warning glare that was clearly threatening her with something terrible if she tried to rescue the file from its fate.

His sockets went completely dark. “D o n ' t . T e l l . A n y o n e .” he warned, still glaring at her.

She blinked, and then he was gone.


	2. Closely Guarded

**Notes for the Chapter:**

> How to burn your cinnamon roll

Papyrus, meanwhile, was in another part of the Core, transporting some bits and pieces of machinery that had come from a grand, but now-useless machine Alphys had wanted dismantled for spare parts. It was tedious work, but at least it was useful, and something to do. Something that could help him take his mind off of how unexpectedly eerie the powered-down Core had turned out to be.

Maybe it was just his imagination, or maybe traces of the eldritch energies it had once generated still clung to the vast powerhouse's walls, but there was something really freaking weird about the place. He couldn't shake the feeling that something was wrong with it- that there was something, anything, lurking in its shadows.

Inwardly he scoffed at himself. He, the Great Papyrus, had vanquished dozens of foes without showing fear and against all odds had survived dwelling in the Underground long enough to reach the Surface; what business did he have getting spooked by poor lighting? The skeleton resolved to ignore the- er…- the whatever it was; but he also quickened his pace as he headed down a long corridor.

A sudden movement in the darkness down at the far end made him jump. He growled, annoyed more at himself than at the bizarre thing, and stomped purposefully onward. As he went on, he saw a shadow flicker again, but he paid it no heed; it was only when the something moved a third time, and close by at that, that he finally halted.

“WHO'S THERE?” he snapped.

As he peered into the shadows he began to make out a vague misshapen form, whose writhing edges were impossible to see distinctly. When he got no reply from it, Papyrus took a few steps nearer, and the indistinct thing seemed to draw itself up to its full height, looking down at him with an eyeless face. Papyrus tensed, ready to drop what he was carrying and start whaling on the stranger the second it showed any sign whatsoever of being a threat.

The standoff persisted for a few minutes, until finally the amorphous thing twitched as if it were cocking its head, made a sound like a sigh, and slunk away. Papyrus watched as it retreated down another corridor with bated breath, until finally it disappeared altogether.

He shuddered involuntarily and carried on, frequently glancing back over his shoulder and puzzling over why he felt he'd seen the thing before. Surely he would've remembered such an encounter; it must have been ages ago. For all he knew it had happened way back when life Underground was just beginning to degrade. Strangely, the one thing that kept cropping up in his mind was the day that he had first gained in execution points.

His memories of the fight were nebulous; even at the time it had all been a blur, a tempest of fury and whirling bullets. Usually, in their younger days, Papyrus was the one who had needed saving; even as people grew steadily more hardened and spiteful and less willing to forgive weakness, he hadn't wanted to be mean back. A year ago, he would have called his past self pathetic for so stubbornly trying to be friendly, or at least not unpleasant, but now he wished he could've stayed that way.

That got him into a lot of trouble as a kid. For a few years, Sans had always been there, keeping watch and warding off anyone who tried to bully him- or worse. But for some reason, after a while Sans kept having to go off somewhere and do something else- Papyrus couldn't remember what, he hadn't understood it then and understood it even less now- and he'd been forced to learn to fend for himself. It was either fight back until they backed off or get ground to dust.

But while Papyrus grew stronger just by growing up, without even gaining any LOVE, Sans never seemed to, stats forever stuck at straight ones. And as the situation Underground grew steadily worse, he started looking like an easy target for thugs out for free EXP.

And so it was that Papyrus's turn came to rush into a brawl.

Someone- he didn't know who, didn't know why, he couldn't even recall their face, they were just a looming threat in his mind- just suddenly attacked Sans out of nowhere while Papyrus was messing around a few yards away. Even then Sans had been good at dodging and giving as good as he got, but the abruptness of the attack had thrown him off, allowing several strikes to get dangerously close to hitting him. And by the look of things the other monster was slugging bullets with the intent to kill, all while Papyrus looked on in horror. Something snapped within him- forget reasoning, forget waiting until they backed off, he would do whatever it took.

He hadn't been thinking clearly, driven on solely by fury at the thug and terror of losing his brother. He'd just charged in screaming and started pounding the mugger with bones. Distracted, the other monster let Sans alone and turned their attention to Papyrus, and that was their undoing. When he saw his little brother in danger Sans began fighting even harder, and before the thug knew what hit them both skeletons were working in tandem to bombard them with attacks- a hailstorm of white and pale blue bullets, bones wielded as clubs or sharpened like skewers, and even beams of magic from their Blasters, taking turns throwing the thug around with their blue magic.

Even as the other monster's counterattacks began to peter off and finally stopped completely, the brothers' instincts howled at them to keep going. They kept up the barrage for what felt like an eternity, hardly aware anymore of what they were doing as they fought on despite all reason, until suddenly Papyrus reached out to grab their soul again with blue magic and found- nothing. Sans must have realized it, too, because he suddenly froze up, sockets listless and dark. A final stray bullet struck the ground, and kicked up dust.

The younger skeleton gaped at the torn-up ground in shock, and shuddered with revulsion before his knees gave out and he sank to the ground. He became suddenly aware of a sharp pain around his left socket that soon began to throb- caught up in the heat of the moment, it hadn't even registered that he'd been hit so much.

Papyrus wanted to sob over what had just happened, to tell his brother he was _so_ glad he was okay, or thank him for sticking with him in the fight instead of running away, or ask him to take them home now, or to just… sit and wait for the hollow look on Sans's face to go away. His jaw twitched as he began to speak- but no. There, not far away, watching them with arms crossed, wearing masks of apathy that poorly veiled their interest in the outcome, were older monsters. They'd clearly seen the whole fight, or at least enough of it, and wanted to see the whole thing play out to its end. This was _not_ the time to show weakness.

So instead, Papyrus said the first thing that came to mind.

“TH-THAT WAS PATHETIC!” he spouted, hardly realizing what he was saying. It was all he could do to stop his bones rattling from how much he thought he was trembling. “W-WE COULD'VE TAKEN THEM OUT FASTER THAN TH-THAT!” He thought he'd yelled something more, but Papyrus couldn't remember what. The specifics didn't matter.

Pain and confusion filled the hollowness in Sans's expression, and Papyrus, turning his back to the other monsters, looked at his brother pleadingly, willing him to hear- _just play along, please_. Understanding crossed the other skeleton's face, quickly replaced by a guise of irritation.

That had been the charade they'd kept up for years, first letting it drop when there was no one else in sight, then only when they were in the safety of their own shelter, then… never. Eventually, Papyrus mused uneasily, as his thoughts strayed from that first battle to the day Frisk came, and Sans told him exactly what he thought of him, in the end they'd stopped treating it as a charade at all.

But how did the shadow thing come into it all?, he wondered. No, there was more to the shade than that, something that his gut instinct told him was worse. A different brand of horrifying than that terrible day, maybe something that had happened shortly after. Papyrus wracked his brains for the answer, but although he felt that the answer was almost within his grasp he soon gave up. If it was indeed something just as distressing, then maybe some things were best left forgotten.


	3. Closely Watched

Sans hadn't gone far from the workshop; he knew it was probably just paranoia, but he didn't want to risk trying to take too many shortcuts. He knew who haunted the Core, and the crossover had shown Sans that _he_ was still perfectly capable of meddling with things better left alone.

So he took the long way out, navigating his way through the labyrinthine building that he still knew depressingly well. The file was stuffed under his jacket, in case he bumped into someone else- it would only prompt uncomfortable questions. Hopefully Alphys would keep her freaking mouth shut. He personally wouldn't put it past her to try to keep on snooping when she thought no one else would know- but she wouldn't uncover anything.

The file was the last thing he hadn't been able to find when he'd fled the Core with Papyrus. Once Sans discovered that no one else remembered Dr. Gaster, he knew it was only a matter of time before they were kicked out onto the streets with nothing to their names, or worse. He'd dropped his brother off in Snowdin, near the secret workshop, before going back and gathering up their belongings- and their vanished fathers' research. If only his search hadn't been so rushed… Finding his file was the main reason why he'd agreed to go back to the Core now. It was the last loose end and finally, it was in his grasp.

Now he just had to decide what to do with it. He'd told Alphys he'd destroy it mostly to keep her from sticking her nose where it didn't belong. It was a tempting idea, but… even now, that they'd reached the surface and were ostensibly trying to put their past behind them, some habits died hard.

Sans walked unsteadily on with his fists clenched tightly in his pockets. He hadn't felt _this_ agitated in a long while. The hallways he walked now weren't arranged the way they had been when he'd last been in the Core, but everything felt achingly familiar nonetheless. Finally finding the file wasn't helping.

Old memories crowded inside his skull as he went.

After the deaths of the King's children, Asgore in a fit of angry grief had pressured his Royal Scientist to work even harder to break the barrier, to prepare for a war with the humans, to find ways to make monsters stronger, to… do basically everything, really. The King's demands set the bar very high, and he brooked no disappointments.

Soon, Sans's father's work claimed his life, shoving everything else to the sidelines.

Sans, meanwhile, was left in a bind. When he was younger he'd been interested in the doctor's research, and for that he'd gotten roped into becoming his lackey-slash-test subject. Sans's memories of Dr. Gaster's experiments were unpleasant ones; even his earliest ones, from before the Underground went mad, were starting to sour, tainted by the knowledge of what had come after.

A _very_ few times early on, he'd tried to flee, to get out of doing experiments- or being experimented on. His reactions then hadn't been as quick as they were now- so before he could run or slip away through cracks in time and space the Royal Scientist would round on him, while his soul would burn blue and anchor him in place, cutting off his escape. Sans tugged nervously at his collar; he'd soon learned to give up on defiance.

At other times, it seemed he could never keep up with the hurried Royal Scientist, and would feel the pull of blue magic forcing him along. It was a dismaying feeling. It didn't feel like being dragged along, as one might've expected; no, it was more his soul was suddenly free-falling toward the direction of the blue magic's pull, yanking him along with it, down corridors so very much like the one he was currently walking in. He could practically feel himself plummeting now.

At least he wasn't still in the hidden testing room. Dr. Gaster's research spanned many topics, and he carried it out in equally diverse places. The older skeleton's endeavors in generating and harnessing magical energies were, naturally, carried out in the Core itself. Investigations into space and time, meanwhile, were typically conducted in the secret workshop he'd built beneath Snowdin Town, away from the potential interference of the Core's magic. His study of how to change monsters' magic he'd carried out in the deep laboratories beneath Hotland.

But in that hidden room in the Core, the Royal Scientist had devised all of his hypotheses and experiments- and tested a select few, away from prying eyes. No one else could be allowed to discover that Sans's stats were beyond pathetic, after all.

Some tests worked better than others. Retribution and manipulating space, at least, worked without a hitch. But as they continued it became clear that they were going one step forward and two steps back, to the Royal Scientist's eternal frustration.

On one occasion- well, only one that he knew of- Sans nearly died there. As Dr. Alphys discovered later with her own experiments, sometimes, a monster's stats would suddenly plunge rather than rise while their magic was being messed with. Sans, of course barely had anything to begin with and- well.

He came to a few days later. The experiments were put on hold. The older skeleton actually seemed concerned over his well-being for the first time in forever. Then, a few weeks later, the accident happened, putting further tests off forever.

When Sans hadn't been stuck dealing with experiments, he'd tried to watch out for his brother. Someone needed to, and Dr. Gaster certainly wasn't. And considering how frequently the older skeleton pulled Sans away to the Core, even he hadn't been able to do as much as he would've liked. Sans occasionally found himself vainly wondering what the Royal Scientist would have done years ago, if he'd bothered to look up from his work for a second and saw what was going on outside the Core. Once upon a time in the days before things got really bad he probably would've cared enough to step up, do _something_ to protect Papyrus. By the time Dr. Gaster did take notice of his younger son again, the damage was already done.

The Royal Scientist always kept a close eye on everything that went on within the Core. Virtually nothing was permitted to escape his notice- it always seemed like the Royal Scientist knew what Sans was doing practically before Sans did himself. Even now, Sans found himself having to resist the urge to look over his shoulder to see if the older skeleton was coming up behind him, and half-expected to find the Royal Scientist awaiting him at every turn. Dr. Gaster had used his powers to make it seem as if he could be everywhere at once, to keep his employees- and, more importantly, Sans- on their toes, and keep them from so much as speaking a word against him. His father's habit of suddenly appearing out of nowhere when he wanted to confront someone had been very discomfiting, particularly in the days before Sans himself had learned about shortcuts.

So naturally, after his and Papyrus's first… real fight, the older skeleton had immediately noticed that Sans had reached level two. Sans let out a tired sigh at the memory. _in spite of acting like he knew everything that went on in the core, it took the stupid_ _dastard_ _a whole friggin' week to notice papyrus was_ also _level two_ , the skeleton thought bitterly. That was one of the few things that had ever noticeably stunned the typically collected scientist. But nevertheless he'd done nothing; if Dr. Gaster had still cared, then he evidently didn't think there was a point in trying to intervene anymore.

Sans's thoughts were thankfully yanked out of the past when he saw that he was nearly out. Just down the hallway, past the entrance of another corridor, were the elevators. Relief flooded through the skeleton as he hurried toward them.

Out of habit, he cast the second corridor a sideways glance as he passed it- and froze in his tracks. He turned his head, until he was staring down a vaguely-skeletal phantom. It started shuffling toward him. Sans's vision immediately flooded with red as he rounded on it, and the shade fortunately took the hint. For a moment they regarded each other. As the silence dragged on the shade uncertainly started raising its hands, as if in surrender.

Sans gritted his teeth. He pulled his right hand out of his pocket, and after only a moment's doubt the shade became tinged with blue, and Sans flung the remnant of Dr. Gaster away with all of his might. The short skeleton waited for a tense moment to see if it would come back, sockets open wide with disbelief. Finally, as nothing else horrible emerged from the darkness of the Core, Sans turned and ran down the hallway to the elevator.

It was time to leave all of that behind.

**Notes for the Chapter:**

> The ending of this chapter was really hard to pin down; I considered having it end with Felsans doing all the recollecting at his house back at the Surface, or with him actually destroying the file and then... I don't know what would've come after that, and so on before I finally hit on this.


End file.
